Conventional dishwashing pastes are liquid or gel-like compositions that are suitable for forming hardened dishwashing agents that have a similar look and feel to that of a bar of soap. Once the pastes are formed, their chemistry allows them to harden to a desired hardness level for packaging and sale to customers. Such hardened dishwashing agents are popular in the developing world.
Current dishwashing paste compositions are typically formed of a high amount of abrasive/filler material, such as calcium carbonate, that is suspended in a viscous solution which includes surfactant(s), sodium carbonate, and sodium silicate, as well as other additives. The surfactants provide the foaming and cleansing properties of the dishwashing agent, while the sodium carbonate helps to adjust the pH level of the formula. The sodium silicate is the primary component that allows the composition to harden by providing silica that polymerizes when mixed with the other components.
Dishwashing pastes typically must achieve some desired level of hardness after they are packaged and before they are sold to consumers, which is generally about 5 mm penetrability. On the other hand, the pastes should not harden to such an extent over time that they exceed the threshold hardness value, or they will develop a “rock-like” texture and become unsuitable for their intended use. The mechanism by which conventional dishwashing paste compositions achieve the desired level of hardness is through the polymerization of silica, as alluded to above. The primary cation component present in conventional formulas is a monovalent sodium cation. The alkaline pH of the composition (modified by the sodium carbonate) causes the silica surface charge to become more negative by hydroxyl ion adsorption, as well as by surface silanol group ionization. These changes in the silica surface cause mutual repulsion between the colloidal silica particles present in the solution, thus slowing their polymerization. The monovalent sodium cation allows polymerization to occur by shielding the negative charge. However, current polymerization processes are slow and inefficient, and some conventional hardened dishwashing agents have a tendency to over-harden, resulting in rock-like texture through the time, which is not well perceived by the consumers.
To solve this problem, dishwashing paste compositions have been prepared in the industry that achieve the requisite level of hardness without developing “rock-like” texture. However, these formulas tend to increase the quarantine time required for the formula to reach the desired level of hardness. This is undesirable because it requires increased inventories at manufacturing sites, reducing inventory rotation and thus increasing associated manufacturing costs.
As such, a dishwashing paste composition that achieves a target hardness more quickly, while maintaining that hardness for an extended period of time thereafter without developing a “rock-like” texture is desired.